1. Field of the Invention
The present invention relates to a solvent recovery treatment method for recovering an evaporated solvent by using an adsorbing agent in a filming process, a coating process, etc. using an organic solvent in a chemical factory.
2. Description of the Related Art
Examples of a process producing at least two or more kinds of solvent-gas containing gases which are different in gas concentration include a filming process, a coating process, etc. As a solvent recovery method for treating a solvent produced in those processes, there has been a method in which, as shown in FIG. 2A, solvent-gas containing gases from a rarefied solvent gas producing source 1 and a dense solvent gas producing source 2 are respectively cooled in coolers 3 and 4, mixed by blowers 5 and 7, and then fed to an adsorbing device 9b, so that the solvent of the mixture is adsorbed by an adsorbing agent 10b while the gases of the mixture are discharged. Alternatively, the gases of the mixture may be circulated by blowers 6 and 8 through filters 14 and 15 respectively so as to be used again. On the other hand, in this method, a heat regeneration gas 11 is fed to an adsorbing device 9a so that the solvent adsorbed in the adsorbing agent 10a is released from the adsorbing agent 10a, and then the thus released solvent is condensed in a condenser 12 so as to be recovered into a solvent storing tank 13. The adsorbing devices 9a and 9b are made to continuously alternately adsorbing and releasing recovery by switching respective valves 16.
Besides, there has been another recovery treatment method in which, as shown in FIG. 3A, an adsorbing device for a rarefied solvent gas producing source 1 and another adsorbing device for a dense solvent gas producing source 2 are provided separately to thereby adsorb and release a gas of a single solvent gas concentration in the same manner as in FIG. 2.
In FIG. 3A, where reference numbers found also in FIG. 2A denote elements analogous to those of FIG. 2A, a rarefied solvent gas producing source 1 and a dense solvent gas producing source 2 are respectively cooled in coolers 3 and 4, mixed by blowers 5 and 7, and then fed to a first adsorbing device 9a and a third adsorbing device 9c. Thereby the solvent of the mixture is adsorbed by first and third adsorbing agents 10a and 10c, respectively, while the gases of the mixture are discharged. Alternatively, the gases of the mixture may be circulated by blowers 6 and 8 through filters 14 and 15, respectively, so as to be used again. In this method, a heat regeneration gas 11 is concurrently fed to second adsorbing device 9b and a fourth adsorbing device 9d, so that the solvent adsorbed in the second and fourth adsorbing agents 10b and 10d is released therefrom. The thereby released solvent is condensed in first and second condensers 12a and 12b, respectively, so as to be recovered into first and second solvent storing tanks 13a and 13b, respectively. By switching valves, the first adsorbing device 9a is made to continuously alternate adsorbing and releasing recovery processes with the second adsorbing device 9b. Similarly, the third adsorbing device 9c continuously alternates adsorbing and releasing recovery processes with the fourth adsorbing device 9d.
However, in the method shown in FIG. 2A, the adsorbing faculty of an adsorbing agent is reduced because of mixing a dense gas and a rarefied gas. Otherwise, in the method shown in FIG. 3A, because of providing two pairs of adsorbing devices, the equipment rate has been high, and the regeneration cost per unit solvent treatment has been increased. The cost per unit solvent treatment increases with the frequency with which regeneration is performed. Therefore, as explained with reference to FIGS. 3B(1) and 3B(2) hereinafter, use of the arrangement shown in FIG. 3A is not cost-efficient, because the adsorption efficiency of the rarefied gas is less in comparison with that of the dense gas, resulting in shortened regeneration cycles.